915 transmission sudden issue - 1st and reverse now grind upon engagement

[p911dad]

As the title suggests, our 1984 Carrera's tranny is making some unwelcome noises. It went from being easy to engage in first and reverse to dragging, balking and grinding in only a few hundred miles from when it was perfect. I have to double clutch to get it into 1st or reverse. The tranny was professionally adusted by a local expert last year and the couple replaced and adjusted perfectly. The car is driven seldom, fluid level is fine. Never abused. It has 100,000 miles. Any ideas or suggestions?

[timmy2]

Check the coupler adjustment before anything else.
Perhaps motor mounts or transmission mounts are failing?

[RedCoupe]

How's the clutch adjustment? If it's got too much free play it might not be completely disengaging.

[Arne2]

I'm thinking clutch also. Doesn't sound quite like a coupler issue.

[DRACO A5OG]

+1 check the clutch and maybe the shifter bushings???

[p911dad]

Thanks all. I will start with the clutch adjustment

[jlex]

Sounds like your clutch cable is getting ready to break. I'd adjust it, then if it stretched again I'd suspect it's getting ready to break.

[cabmandone]

Does the shifter feel sloppy? I had about the same problem and it ended up being the shift rod bushing in the tunnel had disintegrated. I know you said the coupler was replaced but the tunnel bushing and the shift cup bushing could need to be replaced also.

[gomezoneill]

Clutch cable stretched and ready to break or the T/O bearing fork ready to let go.

[KTL]

Originally Posted by gomezoneill

.........or the T/O bearing fork ready to let go.

Yep that problem can cause people to chase their tail so to speak. Adjust the clutch cable, works for a little while, then it's out of adjustment again. What happened? Crack in the fork where it joins with the clutch release shaft

Clutch/Flywheel Analysis

[cabmandone]

Originally Posted by KTL

Yep that problem can cause people to chase their tail so to speak. Adjust the clutch cable, works for a little while, then it's out of adjustment again. What happened? Crack in the fork where it joins with the clutch release shaft

Clutch/Flywheel Analysis

I saw a thread recently where the clutch arm that mounts on the splined shaft had cracked. I still think I'd check the tunnel bushings as mine just decided to start grinding one day and it was because the shift rod bushing was gone. It doesn't take much play to bump a gear and grind and that shift rod busing will allow A LOT of play.

[Bob Kontak]

Originally Posted by cabmando

I saw a thread recently where the clutch arm that mounts on the splined shaft had cracked. I still think I'd check the tunnel bushings as mine just decided to start grinding one day and it was because the shift rod bushing was gone. It doesn't take much play to bump a gear and grind and that shift rod busing will allow A LOT of play.

This is the first think I thought of when OP said it crapped out so quickly.

Something gave up the ghost fast.

[KTL]

No argument here with cabmando or Bob K.

As you can see, there's quite a few scenarios of failure that can cause your problem

[Wew]

If none of those solve your problem, your main shaft bearing may be loose.
Common problem on the 915. How do I know? I had same symptoms and decided to open my transmission up while doing my engine rebuild. After dissembling the nose, where 1st and reverse live, the main bearing and race just fell out. Made sense that I was having trouble with first and reverse as they are the farthest distance from the bearing and housing then the other gears. As long as you are organized take your time and lots of pictures the job is doable. Mine shifts like butter now.

Like the above masters mention, check all of their suggestions first before you go dropping your engine and transmission (do them together, much easier)

Best of luck,

Gary

[KTL]

Actually its 5th and reverse that are contained in the nose case of the transmission. 1st is nearby but it is just next door on the interior side of the main/center case section, right next to the support bearings in the center case.

The bearing race that typically comes loose is the pinion bearing race- the really big one on the bottom. Seems logical that this bearing race can loosen up since it is supporting the pinion shaft where power transfer is occurring immediately nearby at the pinion gear head and ring gear.

[Ryce Stallings]

Just went through this, you could have a cracked fork. One way to tell is if it shifts clean when the engine is cold. It took a while for the fork to break completely!

[p911dad]

Got the car back today. The mechanic said the clutch was grossly out of adjustment and it may be the clutch fork slowly giving way. However he qualified that by stating this Carrera model has the Turbo clutch fork which is stouter than the SC version. Since the Turbo version pushes a heavier pressure plate, he said it is highly unusual for the Turbo part to fail on a Carrera. Or the adjuster somehow backed out in its threads. He tested it several times for a good distance and then rechecked it, no change. Don't know, I am not an expert. It now shifts like a new car, the first - second syncro is like a dream. Here's hoping its not the clutch fork! Thanks all for your comments. Cost all of $45. labor! Dodged a big one!! (I hope!)

[KTL]

Thanks for the follow up report. Interesting that the mechanic says a 930 fork can be used on a Carrera/915. It wouldn't seem like it works since the fork "offset" doesn't appear to be the same between the two different forks. I would double check with your mechanic that he's correct about the use of a Turbo fork.




Top picture is the 930 fork. You can see the arms are much beefier than the curved 915 arms.

I think the 930 fork must be used with a 930 release bearing. Because the way the forks engage the bearing are quite different. The 930 bearing has ears or tabs on it. The 915 is simply round and the thin fork arms slip into the groove.

930 release bearing



915 release bearing

[cabmandone]

Glad you got it fixed! It seems odd that the adjustment went from really good to really bad in such a short amount of time.

Maybe he meant the release lever?